Hitherto, various fluorine-containing compounds are proposed. The fluorine-containing compounds have the advantageous effects of having properties excellent in heat resistance, oxidation resistance, weather resistance and the like. The fluorine-containing compounds are used as, for example, the water- and oil-repellent agent and soil release agent by utilizing the properties that the fluorine-containing compounds have low free energy, i.e., difficulty in adherence.
Examples of the fluorine-containing compounds used as the water- and oil-repellent agent include a fluorine-containing polymer having repeating units derived from (meth)acrylate ester having a fluoroalkyl group. It is proposed that a (meth)acrylate ester having a spacer which is an organic group positioned between an acrylate group and a fluoroalkyl group is used in the fluorine-containing polymer. Such fluorine-containing polymers having the spacer are disclosed in, for example, U.S. Pat. No. 3,655,732, U.S. Pat. No. 3,773,826, U.S. Pat. No. 3,916,053 and U.S. Pat. No. 5,439,998. These fluorine-containing polymers, however, could not impart sufficient water- and oil-repellency.
Various recent research results indicate that in view of the practical treatment of fibers with the surface treatment agent (particularly the water- and oil-repellent agent), the important surface property is not a static contact angle, but is a dynamic contact angle, particularly a reversing contact angle. That is, the advancing contact angle of water is not dependent on the carbon number of the fluoroalkyl side chain, but the reversing contact angle of water in the case of carbon number of at most 7 is remarkably low than that in the case of carbon number of at least 8. In correspondence to this, an X ray analysis shows that the side chain crystallizes when the carbon number of side chain is at least 7. It is known that the actual water repellency has correlation with the crystallization of the side chain and that mobility of the surface treatment agent molecules is an important factor for expression of the actual performances (for example, MAEKAWA takashige, FINE CHEMICAL, Vol. 23, No. 6, page 12 (1994)). Accordingly, it is believed that the acrylate polymer having low carbon number of fluoroalkyl group in the side chain which is at most 7 (particularly at most 6) has low crystallinity so that the polymer cannot satisfy the actual performances (particularly water repellency).
JP-A-63-90588, JP-A-63-99285 and JP-A-01-315471 disclose that a fluorine-containing acrylate polymer wherein the alpha-position is substituted with fluorine, chlorine or the like has excellent properties such as good adhesion to a substrate, high strength of a film and good water- and oil-repellency. These publications describe that the fluoroalkyl group used in Examples has at least 8 carbon atoms and does not suggest to use the acrylate monomer having the fluoroalkyl group having at most 6 carbon atoms.
Recent study results (EPA Report “PRELIMINARY RISK ASSESSMENT OF THE DEVELOPMENTAL TOXICITY ASSOCIATED WITH EXPOSURE TO PERFLUOROOCTANOIC ACID AND ITS SALTS” and the like clarify that a PFOA (perfluorooctanoic acid) doubtfully has a potential risk of environmental load. EPA (Environmental Protection Agency of USA) announced on Apr. 14, 2003 that the EPA intensifies the scientific investigation on PFOA.
On the other hand, Federal Register (FR Vol. 68, No. 73/Apr. 16, 2003 [FRL-2303-8]) EPA Environmental News for release Monday Apr. 2003 “EPA INTENSIFIES SCIENTIFIC INVESTIGATION OF A CHEMICAL PROCES SING AID”, and EPA OPPT FACT SHEET Apr. 14, 2003 announced that a “telomer”may possibly metabolize or decompose to PFOA. It is also announced that the “telomer”is used in a large number of commercial products including fire fighting foams, care products and cleaning products as well as soil, stain and grease resistant coating on carpets, textiles, paper, and leather.